The present invention generally relates to improvements in electric motors to propel small vehicles, and more particularly, to a novel stator ring construction and heat dissipation structure for such motors.
The use of electric motors as the motoring force and generator for many types of vehicles and devices is desirable as such are pollution free, very quiet in operation, light weight, and can be made compact. With such features, electric motors have progressively been given newer applications. For instance, two-wheel transportation devices such as bicycles, lawnmowers, mopeds, wheelchairs, scooters, and nautical transportation devices, such as personal watercrafts and small boats are all either known to have been propelled by electric motors or have the potential to be. Other applications may include, as examples, transportation devices for the physically challenged and wind turbines.
Electric power has emerged as a popular motoring force generator for some transportation vehicles as they may be recharged during use, whereby such vehicles can become autonomous for long distances. For instance, an electric motor mounted to a bicycle can act as a generator and may be recharged when the bike is going downhill, or when the motor is in a braking mode.
U.S. Pat. No. 6,093,985, issued to Chen on Jul. 25, 2000, discloses an electric motor adapted for powering a bicycle and which consists of a motor housing having a rotor portion mounted to the spokes of a bicycle. The housing and rotor assembly rotate about a mandrill upon which a stator portion is secured. The rotor is an annular wall provided with a magnet layer on its inner surface, whereas the stator comprises a plurality of silicone steel sheets having a coil circumferentially mounted thereon. When the coil is energized, the rotor portion is rotated, whereby the bicycle is driven forward.
In designing an electric motor for the above-described purpose, many considerations must be taken into account. For instance, the electric motor must be able to sustain varying temperatures as it is subject to heat generated from the coils and electronic components as the motor produces electricity. This temperature increase will create thermal expansion of the various pieces in the electric motor and expose electronic components housed with the motor casing to high heat. Therefore, electric motors must be adapted for sustaining thermal expansion of their components and provide excellent heat dissipation. In some applications, the electric motors must remain as light as possible, as the weight thereof is part of the load to be driven. This is especially important for touring applications, which involve peak demands of power, fast accelerations and sudden braking. Furthermore, the motor space is often limited, especially in motor applications where small size is important, such as for motoring bicycles. Finally, some of the above-described transportation devices are relatively inexpensive, and therefore the cost of the electric motor is an important factor to maintain the device price competitive. A good design for an electric motor adapted for touring applications is a compromise between lightweight and heat dissipation. Known electric motors of this type are also costly to assemble due to their complexity of construction and design.
Stators are typically constructed of steel sheet layering, which consists of a plurality of silicon iron sheets of a same shape being stacked and bonded together. Although such stators have high mechanical strength, as well as low electrical resistivity and high magnetic permeability, they are relatively expensive to produce and involve substantial losses of material (i.e., loss of material due to the plurality of layers). Furthermore, heat dissipation is not optimal for such stators, as the heat transfer between iron sheets is weak. Therefore, the heat dissipation of such stators is said to be two-dimensional. Similarly, as these stators consist of stacked sheets, only two-dimensional shapes may be defined. Therefore, these stators are not geometrically optimizeable and exhibit poor heat dissipation.
It is a feature of the present invention to provide a stator ring for an electric motor which substantially overcomes the above-described disadvantages of the prior art.
It is a further feature of the present invention to provide such a stator ring of lightweight construction.
It is a still further feature of the present invention to provide a stator ring for an electric motor capable of having its size varied for increasing its output.
A further feature of the present invention is to provide an electric motor housing design which improves heat dissipation during operation.
Still another feature of the present invention is to provide an electric motor housing design incorporating an electronic circuit board mounted for improved heat dissipation.
A still further feature of the present invention is to provide an electric motor housing design having a circuit board on which are mounted a plurality of mosfet components with the casing of the mosfets secured to a heat sink assembly.
A further feature of the present invention is to provide an electric motor which is easy to assemble at low cost.
According to the above feature of the present invention, and from a broad aspect thereof, the present invention provides a stator ring for an electric motor. The stator ring comprises plural stator ring sections being molded of electrically insulated ferromagnetic powder. The stator ring sections each have an arcuate shoe having at least two teeth projecting radially therefrom. The teeth are adapted for receiving coil windings. The stator ring sections are adapted for being retained end to end by a stator core to form a complete stator ring. The arcuate shoes of the stator ring sections create expansion gaps between opposite ends thereof when the stator core and the stator ring sections are subjected to heat expansion, to prevent damage of the stator ring due to the heat expansion.
According to a further broad aspect of the present invention there is provided an electric motor stator assembly which comprises a stator core having an internal housing defined between an outer cylindrical wall and an inner central hub. Support means is provided for supporting a stator ring having coil windings about the outer cylindrical wall. Passage means is formed between the central hub and the outer cylindrical wall for dissipating heat from the internal housing. Securing means is provided for securing an electronic circuit board having heat generating electronic components in the housing. Conduction means is provided to conduct heat directly from the housing to a support shaft assembly of a wheel of a vehicle being motorized by an electric motor incorporating the stator assembly.
According to a still further broad aspect of the present invention there is provided an electric motor stator assembly which comprises a stator core having an internal housing defined between an outer-cylindrical wall and an inner central hub. A stator ring, having coil windings, is supported about the outer cylindrical wall, Passage means is formed between the central and the outer cylindrical wall for dissipating heat from the internal housing. Securing means is provided for securing an electronic circuit board having heat generating electronic components in the housing. Heat sink means is secured through the circuit board and in contact with some of the electronic circuit components to conduct heat directly from the components to the stator core to non-electrically conductive insulating means.